Efficient coupling of light from one optical fiber to another requires a precise alignment of the cores of the two fibers. In most fiber optic connectors, each fiber is terminated with a cylindrical ferrule. With the core of the fiber centered on the axis of the ferrule, the alignment of two optical fibers is reduced to the alignment of the central axes of the two ferrules.
In order to establish this alignment, the ferrules are usually inserted in opposition in an alignment sleeve within an interconnect housing. Such an arrangement is illustrated in U.S. application Ser. No. 283,288, filed by Harold A. Roberts, on July 14, 1981, incorporated herein by reference and assigned to the assignee hereof. The spacing of the opposed ferrules in the interconnect housing is accomplished by the mating of ferrule flanges with seats machined into the interconnect housing. The travel of each ferrule within the interconnect housing is limited by the mating of the flange with the seat. The distance between opposed seats is such that, taking into account the length of the ferrule from its tip to its flange, a predetermined spacing is established between the inserted ferrules. The precision with which the two ferrules can be spaced-apart is therefore dependent upon the spacing between the opposed seats in the interconnect housing and the individual lengths of the ferrules themselves. In terms of manufacturing, the degree of precision attainable by the machining of seats into an interconnect housing is not always high enough to assure that the ferrule tips will not come into contact when inserted into the interconnect housing, nor is the accuracy always high enough to prevent poor optical coupling due to large tip-to-tip spacing.
It will be appreciated that physical contact of two ferrules within an interconnect housing is undesirable because of the possibility of damage to the fiber ends due to scratching or scoring from microparticles or contaminants trapped between the ferrules. On the other hand, the light loss across the fiber-to-fiber joint increases as the fibers are separated. The desired separation is therefore one which is as small as possible, yet non-zero, so as to eliminate any possibility of the ferrule tips touching when thrust into an interconnect housing. Typically the separation should be larger than a typical dust particle and should therefore be greater than 0.0001 inch.
Thus a consideration in the design of an interconnecting mechanism for joining two optical fibers terminated by a ferrule is the provision of a very small repeatable non-zero separation between the ferrule tips. The determination and maintenance of the separation is, however, not a trivial problem due to the machine fabrication of the parts involved.
Another problem in the manufacture of a suitable interconnect is the provision of an alignment sleeve within the interconnect housing. For some applications a floating or loosely carried sleeve, such as described in the abovementioned patent application, is desirable to permit looser tolerances for the connector housings. However, capturing an alignment sleeve within an interconnect housing is also a non-trivial manufacturing problem.
Moreover, as the size of alignment sleeves is reduced to accommodate ferrules having reduced diameter tips, the small sleeves have become very difficult to handle and can fall out of the interconnect housing. Thus, a still further problem with prior interconnects is the problem of providing a small alignment sleeve in the interconnect housing, in which the alignment sleeve does not fall out either during manufacture or use.